Meteorologische Zeitschrift, Vol. 14, No. 5, 663-669 (October 2005) (published online 2005) c  by Gebrüder Borntraeger 2005 Article Backscatter lidar observation of the aerosol stratification in the lower troposphere during winter Bise: a case study V ALENTIN MITEV ∗1 ,RENAUD MATTHEY 1 ,MAX FRIOUD 1 ,MANOJ K. SRIVASTAVA 1,4 , SABINE ECKHARDT 2 and ANDREAS STOHL 2,3 1 Observatory of Neuchâtel, Neuchâtel, Switzerland 2 Department of Ecology, Technical University, Munich, Germany 3 Present affiliation: Norwegian Institute for Air Research (NILU), Kjeller, Norway 4 Present affiliation: Aryabhatta Research Institute of Observational Sciences (ARIES), Uttaranchal, India (Manuscript received December 18, 2004; in revised form May 19, 2005; accepted May 20, 2005) Abstract This work presents observations of the aerosol mixed layer in the planetary boundary layer and aerosol layers in the lower troposphere during a case of winter Bise wind. The Bise wind event occurred from December 5 till December 18, 2001. The observations were performed above Neuchâtel, Switzerland, 47.00 ◦ N, 6.95 ◦ E, 488 m asl, using a ground-based backscatter lidar, operating at a wavelength of 532 nm. The height of the aerosol mixed layer was found to extend up to 0.6–0.8 km agl. Another aerosol layer centred around 1.5 km and 2.5 km agl was also observed. The combination of the lidar-observed profiles with radiosonde measurements from Payerne station shows a coincidence of the altitudes of the observed aerosol layers with the altitudes of the Bise wind layer. Back trajectories were used to trace the incoming Bise air masses showing a likely origin from North America. Zusammenfassung Diese Studie präsentiert Beobachtungen von Aerosolen in der planetaren Grenzschicht und in der freien Tro- posphäre während Bise-Bedingungen. Das diskutierte Bise-Ereignis fand in der Periode vom 5.–18. Dezem- ber 2001 statt. Die Aerosol-Beobachtungen wurden mit einem bodengestützten Rückstreulidar bei einer Wellenlänge von 532 nm in Neuchâtel, Schweiz (47,00 ◦ N, 6,95 ◦ E, 488 m über NN), gemacht. Die Höhe der Mischungsschicht, abgeleitet aus den Aerosolbeobachtungen, betrug etwa 0,6–0,8 km über NN. Eine weitere Aerosolschicht wurde zwischen 1,5 und 2,5 km über Grund beobachtet. Der Vergleich der Lidar- Profile mit Radiosondenmessungen aus Payerne belegt, dass die Höhe der Aerosolschichten mit der Höhe der Bise-Winde übereinstimmt. Rückwärtstrajektorien zeigen, dass die Aerosole in den Bise-Luftmassen ihren Ursprung vermutlich in Nordamerika gehabt haben. 1 Introduction Recently a number of studies combined backscatter li- dar data with back trajectory analysis of the probed air masses to present the aerosol backscatter altitude pro- files with respect to long-range aerosol transport. Exam- ples for such studies are KREIPL et al. (2000), MAT- TIS et al. (2000), HEINTZENBERG et al. (2003), ANS- MANN et al. (2003) and WANDINGER et al. (2004). The objective of this work is to present observations of the altitude profile of the aerosol backscatter coefficient (further “aerosol backscatter” or ABC) in the Planetary Boundary Layer (PBL) and the free troposphere during one case of winter Bise. This objective is motivated by previously expressed hypothesis that the Bise wind may transport air pollutions (FURGER et al., 1989; WANNER and FURGER, 1990). ∗ Corresponding author: Valentin Mitev, Observatory of Neuchâtel, Rue de l’Observatoire 58, CH-2000, Neuchâtel, Switzerland, e-mail: valentin.mitev@ne.ch The synoptic conditions leading to Bise wind and Bise climatology are well described elsewhere (WANNER and FURGER, 1990; WEBER and FURGER, 2001). The ‘Bise’ is a synoptically induced regional northeastern wind system in Switzerland. It affects the Swiss Middleland (SM) and is channelled between the Alps and Jura. The basic cause of Bise is a northeast- southwest (NE–SW) pressure gradient of the order of 1 hPa / 100 km or more at the 850 hPa pressure level. The Bise substantially decreases the surface tem- perature along its pathway. The highest frequency of Bise winds occurs during winter (Nov–Dec–Jan–Feb) when the synoptic-scale forcing is strongest, followed by spring (Mar–Apr–May), summer (Jun–Jul–Aug) and autumn (Sep–Oct). Bise events typically last for about 3–4 days but sometimes can persist for more, if the synoptic situation remains unchanged. The observations presented here were performed during the case of Bise wind between December 5 and December 18, 2001. The measurements of the ABC profile and the aerosol DOI: 10.1127/0941-2948/2005/0046 0941-2948/2005/0046 $ 3.15 c  Gebrüder Borntraeger, Berlin, Stuttgart 2005